Image processing apparatuses having a function of detecting “edges” in picked-up images are wisely used in various areas; these “edges” means the boundaries at which the image brightness or the color changes. One type of such image processing apparatuses for example disclosed in Japanese Patent Application Publication No. 2001-005966 is designed to cause an image pickup unit to perform a previously determined number of, such as three or more, image pickups while changing the exposure amount of the image pickup unit. The number of image pickups has been previously determined for each of luminance (brightness) ranges of targets to be picked up.
Because the exposure amount of the image pickup unit is changed at the previously determined number of image pickups, it is possible to achieve images with large dynamic ranges relative to the dynamic range of the image pickup unit. Note that the dynamic range means the range between the maximum illumination intensity and the minimum illumination intensity of images that an image pickup unit can pick up.
Thus, even if areas in picked up images are different in luminance from each other, it is possible to detect edges in the picked-up images; these areas correspond to, for example, sunny and shaded regions to be picked up.
However, such an image processing apparatus of this type always needs to perform the previously determined number of image pickups for the luminance range of each target to be picked up, and to perform image processing based on each of the picked-up images so as to detect edges. This may cause, even if there is no need to perform the previously determined number of image pickups, the image processing apparatus to perform the previously determined number of image pickups for the brightness range of each target to be picked up, and to perform image processing based on each of the picked-up images so as to detect edges.
This therefore may increase processing loads of the image processing apparatus upon detection of edges.